In the US and other countries, policy limiting duty hours in graduate medical education has undergone significant revision in the last decade and become a central point of debate. Evidence from human chronobiology and sleep argues for shorter shifts because fatigue leads to errors. However, evidence from operations research argues for more continuity because patient handoffs also lead to errors and may reduce the effectiveness of education necessary to produce independent clinicians. The evidence from both fields is compelling, resulting in uncertainty regarding how to best configure duty hour standards for fatigue management, high quality patient care, and trainee education. In 2011, the Accreditation Council for Graduate Medical Education (ACGME) imposed more restrictive duty hour standards for all trainees. The new duty hours added that post-graduate year 1 (PGY1) trainees (interns) work no more than 16h duty periods in a day. This change greatly increased the frequency of patient handoffs. As a result, alternative work schedules have been proposed that combine longer shifts to maintain continuity of patient care with efforts to manage fatigue. We propose a cluster randomized trial of 58 Internal Medicine (IM) training programs to compare the current duty hour standards (Curr throughout this proposal) with a more flexible schedule (Flex) that is grounded in contemporary understanding of sleep and patient safety and defined by three rules: [1] work no more than 80 hours per week; [2] call no more frequent than every 3rd night; [3] 1 day off in 7-all averaged over 4 weeks. Our primary hypothesis addresses patient safety: 30-day patient mortality under Flex will not exceed (will not be inferior to) mortality under Curr. Our secondary hypotheses address education and sleep and fatigue: (a) Interns in Flex will spend greater time in direct patient care and education compared to interns in Curr; (b) Average daily sleep obtained by interns in Flex will not be less than (will no be inferior to) that of interns in Curr. iCOMPARE (Individualized Comparative Effectiveness of Models Optimizing Patient Safety and Resident Education) will provide the rigorous comparative effectiveness data essential to setting duty hour policies that optimize quality of care and the competency of our future physicians. Moreover, the same two schedules, Curr vs. the novel Flex scheme, are being compared in the ongoing FIRST trial in residents in general surgery. The combination of well-designed separate trials in both primarily procedural and non-procedural fields will fill the unmet need for a high-quality, generalizable body of evidence to inform national duty hour policy.